Soluble material and process for three-dimensional modeling

ABSTRACT

The present invention is a composition for making a three-dimensional object. The composition comprises a plasticizer and a base polymer, where the base polymer comprises a carboxylic acid, where the composition is soluble in an alkaline solution.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.10/898,814, filed on Jul. 26, 2004, which is a continuation-in-part ofU.S. patent application Ser. No. 10/019,160, filed on Oct. 19, 2001.U.S. patent application Ser. No. 10/019,160 is a national phase ofInternational Patent Application No. PCT/US00/010592, filed on Apr. 19,2000, which claims priority to U.S. Provisional Patent Application No.60/130,165, filed on Apr. 20, 1999. The disclosures of the above-listedapplications are incorporated by reference in their entireties.

BACKGROUND

This invention relates to the fabrication of three-dimensional objectsusing additive process modeling techniques. More particularly, theinvention relates to forming three-dimensional objects by depositingsolidifiable material in a predetermined pattern and providing supportstructures to support portions of such a three-dimensional object as itis being built.

Additive process modeling machines make three-dimensional models bybuilding up a modeling medium, based upon design data provided from acomputer aided design (CAD) system. Three-dimensional models are usedfor functions including aesthetic judgments, proofing the mathematicalCAD model, forming hard tooling, studying interference and spaceallocation, and testing functionality. One technique is to depositsolidifiable modeling material in a predetermined pattern, according todesign data provided from a CAD system, with the build-up of multiplelayers forming the model.

Examples of apparatus and methods for making three-dimensional models bydepositing layers of solidifiable modeling material from an extrusionhead are described in Crump U.S. Pat. No. 5,121,329, Batchelder, et al.U.S. Pat. No. 5,303,141, Crump U.S. Pat. No. 5,340,433, Batchelder, etal. U.S. Pat. No. 5,402,351, Danforth, et al. U.S. Pat. No. 5,738,817,Batchelder, et al. U.S. Pat. No. 5,764,521 and Swanson et al. U.S. Pat.No. 6,004,124, all of which are assigned to Stratasys, Inc. of EdenPrairie, Minn., the assignee of the present invention. The modelingmaterial may be supplied to the extrusion head in solid form, forexample in the form of a flexible filament wound on a supply reel or inthe form of a solid rod, as disclosed in U.S. Pat. No. 5,121,329. Asdescribed in U.S. Pat. No. 4,749,347, modeling material mayalternatively be pumped in liquid form from a reservoir. In any case,the extrusion head extrudes molten modeling material from a nozzle ontoa base. The extruded material is deposited layer-by-layer in areasdefined from the CAD model. A solidifiable material which adheres to theprevious layer with an adequate bond upon solidification is used as themodeling material. Thermoplastic materials have been found particularlysuitable for these deposition modeling techniques.

Examples of apparatus and methods for making three-dimensional models bydepositing solidifiable material from a jetting head are described, forexample, in Helinski U.S. Pat. No. 5,136,515, Masters U.S. Pat. No.4,665,492 and Masters U.S. Pat. No. 5,216,616. Particles are directed tospecific locations in a predetermined pattern as defined by a CAD model,and deposited and built up to construct the desired object.

In creating three-dimensional objects by additive process techniques,such as by depositing layers of solidifiable material, it is the rulerather than the exception that supporting layers or structures must beused underneath overhanging portions or in cavities of objects underconstruction, which are not directly supported by the modeling materialitself. For example, if the object is a model of the interior of asubterranean cave and the cave prototype is constructed from the floortowards the ceiling, then a stalactite will require a temporary supportuntil the ceiling is completed. Support layers or structure may berequired for other reasons as well, such as allowing the model to beremoved from a base, resisting a tendency for the model to deform whilepartially completed, and resisting forces applied to a partiallycompleted model by the construction process.

A support structure may be built utilizing the same depositiontechniques and apparatus by which the modeling material is deposited.The apparatus, under appropriate software control, produces additionalgeometry acting as a support structure for the overhanging or free-spacesegments of the object being formed. Support material is depositedeither from a separate dispensing head within the modeling apparatus, orby the same dispensing head that deposits modeling material. The supportmaterial is chosen so that it adheres to the modeling material.Anchoring the model to such support structures solves the problem ofbuilding the model, but creates the additional problem of removing thesupport structure from the finished model without causing damage to themodel.

The problem of removing the support structure has been addressed byforming a weak, breakable bond between the model and the supportstructure, such as is described in Crump, et al. U.S. Pat. No.5,503,785. The '785 patent discloses a process by which a material thatforms a weak, breakable bond with the modeling material is selected as arelease material. The release material is deposited along the interfacebetween the object and its support structure in a layered fashion or asa coating, permitting the support structure to be broken away afterformation of the object. The support structure may be formed of themodeling material or it may be formed of the release material.

The '785 patent discloses various combinations of materials that may beused as modeling and release materials. For instance, the '785 patentdiscloses that a soluble release material may be utilized, so that anysuch material remaining on the model after the support is broken awaycan be removed by placing the model in a bath. Water soluble wax,polyethylene oxide and glycol-based polymers, polyvinylpyrrolidone-based polymers, methyl vinyl ether, maleic acid-basedpolymers, polyoxazoline-based polymers and polyquaternium II aredisclosed, as well as solvent-soluble acrylates and stearic and azelaicacids. Soluble supports can eliminate scarring of the model surface andthe need to use force in removing supports.

In extrusion based systems, a variation of applying release material inlayers has been implemented, in which the release material is applied inshort bead segments (termed “perforations”) between the supportstructure and the model under construction. The perforations reduceadhesion of the support layer by limiting the area of contact with themodel, to aid in the removal of breakaway supports.

There is a continuing need to provide a support structure that releasesfrom a three-dimensional model without the application of force and thatwill not mar the model surface finish, and that further has goodmechanical strength and is compatible with the modeling process and themodeling material.

SUMMARY

A first aspect of the present disclosure is directed to a supportmaterial feedstock for making a support structure for athree-dimensional object using an additive processing technique. Thesupport material feedstock includes a composition having at least onecopolymer and at least one plasticizer, where the composition is solublein an aqueous liquid. The at least one copolymer includes a plurality ofpendent carboxylic acid groups, and a plurality of pendent ester groups.The support material feedstock also has a filament geometry configuredto be received by a filament-fed extrusion system configured to make thesupport structure in coordination with the three-dimensional objectusing the additive processing technique.

Another aspect of the present disclosure is directed to a method offorming a feedstock for making a support structure. The method includesproviding at least one copolymer having a plurality of pendentcarboxylic acid groups and a plurality of pendent ester groups, wherethe plurality of pendent carboxylic acid groups constitute from about15.0% to about 60.0% by weight of pendent groups of the copolymer, basedon a total weight of the pendent groups of the at least one copolymer.The method also includes combining the at least copolymer with at leastone plasticizer to form a composition, the at least one plasticizerconstituting from about 10% by weight to about 30% by weight of thecomposition, and where the composition is soluble in an aqueous liquid.The method further includes forming the feedstock from the composition,where the formed feedstock has a filament geometry that is configured tobe received by a filament-fed extrusion system configured to make thesupport structure in coordination with a three-dimensional object usingan additive processing technique.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of a model formed by afilament-feed extrusion apparatus using the alkali-soluble material ofthe present invention as a support structure.

FIG. 2 is a perspective view (portions broken away) of the model of FIG.1 in an alkaline bath used in practicing the process of the presentinvention.

DETAILED DESCRIPTION

The process of the present invention employing an alkali-solublethermoplastic material is applicable for use in three-dimensionalmodeling systems which deposit molten modeling material that solidifiesto form an object.

The present invention is described with reference to a depositionmodeling system of the type disclosed in U.S. Pat. Nos. 5,121,329 and6,004,124, which are hereby incorporated by reference as if set forthfully herein. In the described embodiment, the modeling material and thesupport material are deposited as substantially continuous strandslayer-by-layer from an extrusion head and are supplied to the extrusionhead in the form of a flexible filament. It will be understood by thoseskilled in the art that the invention can be practiced with advantage invarious other types of modeling machines as well, and that the materialsmay be supplied in alternative forms, such as a liquid, solid rod,pellet or granulated form.

FIG. 1 shows an extrusion apparatus 10 building a model 26 supported bya support structure 28 according to the present invention. The extrusionapparatus 10 includes an extrusion head 12, a material-receiving base14, a filament supply spool 16 and a control 18. Examples of suitablesystems for the extrusion apparatus 10 include Stratasys FDM® systems,such as Stratasys FDM® 1650, Stratasys FDM® 2000, Stratasys FDM® Titan,Stratasys FDM® Vantage, and Stratasys FDM® Maxum; and “Dimension SST 3DPrinter”; all available from Stratasys, Inc., Eden Prairie, Minn.

Extrusion head 12 moves in X and Y directions with respect to base 14,which moves in a vertical or Z direction. Supply spool 16 supplies aflexible filament 20 to extrusion head 12. Filament 20 typically followsa rather tortuous path through extrusion apparatus 10, and is advancedtowards extrusion head 12 by means of stepper motor-driven pinchrollers. Filament 20 is melted in a liquifier 22, carried by extrusionhead 12. The liquifier 22 heats the filament to a temperature slightlyabove its solidification point, reducing it to a molten state. Moltenmaterial is extruded through an orifice 24 of liquifier 22 onto base 14.

The extrusion apparatus 10 of the disclosed embodiment has no positivecut-off valve for stopping flow of the molten material through orifice24 when a layer or a pass is complete. The flow is stopped by ceasing toadvance filament 20 into extrusion head 12. The flow rate at which themolten material is dispensed onto base 14 is determined by a combinationof the orifice size and the rate at which filament 20 is advanced intoextrusion head 12.

The movement of extrusion head 12 is controlled by control 18 so as todeposit material onto base 14 in multiple passes and layers to buildthree-dimensional model 26 having a shape determined by stored CAD dataand further to build support structure 28 defined so as to physicallysupport the model 26 as it is being built. The model 26 and its supportstructure 28 are built up on the base 14 within a build envelope havingan environment controlled to promote solidification. A first layer ofthe deposited material adheres to the base so as to form a foundation,while subsequent layers of material adhere to one other. A base that hasbeen successfully used is a polymer foam removably mounted to aplatform. Other materials that may serve as a base include sandpaperformed of a fine wire mesh screen coated with sand and adhered to aplatform, a water-soluble wax, a foam plastic material, and an acrylicsheet mounted to a vacuum platen.

A modeling material A is dispensed to form the model 26. Analkali-soluble support material B is dispensed in coordination with thedispensing of modeling material A to form the support structure 28. Forconvenience, the extrusion apparatus 10 is shown with only one filamentsupply spool 16 providing a single filament 20. It should be understood,however, that in the practice of the present invention using afilament-feed apparatus such as disclosed herein the modeling material Aand the alkali-soluble support material B are provided to the extrusionapparatus 10 on separate filament supply spools. The extrusion apparatus10 may then accommodate the dispensing of two different materials by:(1) providing two extrusion heads 12, one supplied with modelingmaterial A and one supplied with modeling material B (such as isdisclosed in the '124 patent); (2) providing a single extrusion headsupplied with both the modeling material A and the alkali-supportmaterial B, with a single nozzle for dispensing both materials (such asshown in FIG. 6 of the '329 patent); or (3) providing a single extrusionhead supplied with both materials, with each material dispensed througha separate nozzle (such as shown in FIG. 6 of the '785 patent).

Modeling material A is typically a thermoplastic material that can beheated relatively rapidly from a solid state to a predeterminedtemperature above the solidification temperature of the material, andpreferably has a relatively high tensile strength. Anacrylonitrile-butadiene-styrene (ABS) composition is one particularlysuitable modeling material. Other materials that may be used for themodeling material A include a variety of waxes, paraffin, a variety ofthermoplastic resins, metals and metal alloys. Glass and chemicalsetting materials, including two-part epoxies, would also be suitable.

Alkali-soluble support material B of the present invention is athermoplastic soluble in an alkaline solution, as described in moredetail below. Alkali-soluble support material B likewise can preferablybe heated relatively rapidly from a solid state filament to apredetermined temperature above the solidification temperature of thematerial, and solidify upon a drop in temperature after being dispensed.

The soluble support structure 28 created with support material B may beformed in a known manner, such as disclosed in U.S. Pat. No. 5,503,785,which is hereby incorporated by reference as if set forth fully herein.FIGS. 3-5 of the '785 patent illustrate a removable support structure.As shown in FIG. 1 herein, the support structure 28 may be builtentirely out of the support material B. Or, as shown and described inthe '785 patent, the alkali-soluble support material B may form adissolvable joint between the model formed of modeling material A and asupport structure formed of the same material A. The joint can be arelease layer or layers, or a thin coating.

After completion of the model 26, the support structure 28 is removedfrom the model 26 by soaking the model 26 with its attached supportstructure 28 in a bath 40 containing an alkaline solution C. In theembodiment shown in FIG. 2, bath 40 is an ultrasonic,temperature-controlled bath which contains a removable mesh basket 42for holding the model 26. The temperature of bath 40 is set using atemperature control 44. The alkaline solution C is an aqueous solutionthat can be washed down the drain for disposal. The temperature of thesolution C in bath 40 can be heated to speed dissolution of supportmaterial B. An ultrasonic frequency generator 46 having an on/off switchstarts and stops the ultrasonic transmission. The ultrasonic frequencytransmission generates air bubbles which assist in dissolving away thesupport material B by vibrating the model.

Model 26 remains in bath 40 until the support material B dissolves. Thebasket 42 is then removed from bath 40. The basket 42 can be placed in asink and the solution C rinsed off of the model 26 with water and washeddown the drain. Bath 40 has a drain 48 from which a plug is removed todrain the solution C from the bath 40.

As an alternative to removing support structure 28 from the model 26 bydissolving the alkali-soluble support material B in a bath, the supportmaterial may be dissolved using water jets operated by hand or byautomation.

The base 14 may be removed from the model 26 before placing the model inthe bath 40. Alternatively, the base 14 may remain adhered to model 26as it is placed in bath 40. In the latter case, an alkali-soluble basemay be desired, such as an alkali-soluble foam.

The alkali-soluble support material B must satisfy a large number ofmodeling criteria for the particular modeling system in which it isused, relating generally to thermal properties, strength, viscosity andadhesion. As to thermal properties, the alkali-soluble support materialB must not deform at the temperature in the build envelope, so as tomaintain structural fidelity of the model that it supports. It istherefore desired that the alkali-soluble support material B have aglass transition temperature (Tg) at least 10° C. above the buildenvelope temperature. Further, if the glass transition temperature ofalkali-soluble support material B is lower than that of modelingmaterial A, the rate of dissolution of alkali-soluble support material Bmay be increased by temperature control.

The alkali-soluble support material B must have a melt viscositysuitable for the modeling process. In a modeling system of the typedescribed herein, the melt viscosity must be low enough at the liquifiertemperature so that it can be extruded through the orifice of theliquifier as a generally continuous strand or bead and so that depositedstrands or beads of alkali-soluble support material B have little meltstrength, allowing them to lay flat rather than curl up. Melt viscosityis lowered by increasing the temperature in the liquifier. Too high aliquifier temperature, however, can cause material sitting idle in theliquifier to decompose. If decomposed, in the case of an extrusion headthat has no positive cut-off mechanism, support material B will drainuncontrollably from the liquifier into the build envelope, a conditionreferred to as “ooze”. In practice, viscosity may be measured by itsinverse parameter, melt flow. A desirable melt flow index foralkali-soluble support material B is between about 1 g/10 minutes andabout 10 grams/10 minutes, as measured pursuant to ASTM D1238, under aload of 1.2 kg at 230° C., and is preferably between about 5 grams/10minutes to about 10 grams/10 minutes.

To properly support the model under construction, the alkali-solublesupport material B must bond to itself (self-laminate) and bond weaklyto modeling material A (co-laminate). Where the support structure isbuilt up from the base, alkali-soluble support material B mustadditionally bond to the base 14. The acid content in alkali-solublesupport material B of the present invention makes the material fairlysticky, so that it will adequately adhere to a base made of any numberof materials. For example, a polyurethane foam base has beensuccessfully utilized in the practice of the invention.

To produce an accurate model, alkali-soluble support material B mustalso exhibit little shrinkage upon cooling in the conditions of thebuild envelope, or, the shrink characteristics must match those ofmodeling material A. A shrink differential in the materials would causestresses and bond failures along the model/support structure joint.

Alkali-soluble support material B must have sufficient mechanicalstrength in solid form to provide support to a model during itsformation. The alkali-soluble support material B must resist forces bythe modeling material A, or the model will exhibit undesirable curlingand deformation. Additionally, alkali-soluble support material B, whensupplied in filament or rod form, must be strong enough to be shippedwithout breaking. When supplied in filament form, alkali-soluble supportmaterial B must further have the strength and flexibility to be formedinto a filament, be spooled and unspooled, and be fed through theextrusion apparatus without breakage. Similarly, alkali-soluble supportmaterial B supplied in filament form must have sufficient rigidity tonot be deformed by compressive forces during feeding through theextrusion apparatus. A tensile strength on the order of 1000-5000 psi istypically appropriate for deposition modeling applications.

Solubility characteristics required of alkali-soluble support material Bare that it be readily soluble in an alkaline solution (pH 7 or higher)that does not adversely affect the modeling material A. As used herein,a material is “soluble in an alkaline solution” if the material issubstantially dissolvable and/or dispersible in a solution with a pH ofabout 7 or higher and a temperature ranging from about 25° C. to about80° C. It is additionally desirable that the solution be non-toxic andnon-flammable, so that it requires no special handling or disposal byusers.

The alkali-soluble support material B of the present invention iscomprised of a base polymer, which may include a first comonomer (whichcontains carboxylic acid) and a second comonomer that is polymerizedwith the first comonomer (e.g., via free-radical polymerization) toprovide thermal and toughness properties suitable for depositionmodeling. An alkyl methacrylate (including methyl, ethyl, propyl andbutyl methacrylate), or a combination of alkyl methacrylates, is asuitable second comonomer. Other monomers may be used as the secondcomonomer, that achieve the thermal and toughness characteristicsdesired for the modeling system in which the alkali-soluble supportmaterial B will be used. A preferred base polymer is comprised ofmethacrylic acid as the first comonomer and methyl methacrylate as thesecond comonomer.

A desirable amount of the acid-containing first comonomer is 15-60weight percent of the base polymer. The solubility of the alkali-solublesupport material B is due to the carboxylic acid in the base polymer. Asthe acid content of the base polymer increases, the required alkalinity(pH) of the alkaline solution used to dissolve it decreases. Optionally,additional monomers can be incorporated into the base polymer.

The alkali-soluble support material B of the present invention may alsoinclude a plasticizer to attain rheological properties desired for themodeling process. Selection of an appropriate plasticizer depends on anumber of factors. The plasticizer must plasticate the dry base polymerinto a proces sable thermoplastic meeting the desired criteria. Inaddition, the plasticizer must be compatible with the base polymer.Compatibility is determined by polarity, dispersion and hydrogen bondingforces, as shown by Small's solubility parameters of 8.0 or higher,preferably 8.5 or higher (using Small's molar attraction constantmethod), or as shown by Hansen's solubility parameters of 17.0,preferably 17.5 or higher (from Hansen method described in Handbook ofSolubility Parameters, CRC Press (1991). The plasticizer must notexhibit exudation in the form of an oily film on the plasticizedpolymer. The plasticizer must have a low vapor pressure at materialprocessing and modeling temperatures, preferably less than 10 mm Hg at200° C. and less than 20 mm Hg at 250° C. The plasticizer mustadditionally be hydrolyzable, soluble, emulsifiable or dispersable in analkali solvating bath, pH 7 or higher.

A plasticizer reduces viscosity (i.e., increases the melt flow index)and also lowers the glass transition temperature of a polymer. As such,the concentration of plasticizer in the alkali-soluble support materialB desirably provides the desired glass transition temperatures and meltflow indexes discussed above. For example, the thermoplastic solublesupport material B desirably exhibit glass transition temperatures atleast 10° C. above the build envelope temperatures. Similarly, thealkali-soluble support material B desirably exhibits a melt flow indexranging from about 1 gram/10 minutes to about 10 grams/10 minutes(preferably between 5 grams/10 minutes and 10 grams/10 minutes).

The concentration of plasticizer in the alkali-soluble support materialB may depend on a variety of factors, such as the materials used for themodeling material A, the materials used for the base polymer and theplasticizer of the alkali-soluble support material B, the build envelopetemperature, and the desired flow rates of the modeling material A andthe alkali-soluble support material B. Examples of suitableconcentrations of plasticizer in the alkali-soluble support material Brange from about 0.01% to about 50% by weight, based on the total weightof the alkali-soluble support material B. Examples of particularlysuitable concentrations of plasticizer in the alkali-soluble supportmaterial B range from about 5.0% to about 25% by weight, based on thetotal weight of the alkali-soluble support material B.

Plasticizers found to be compatible include plasticizers in the generalclasses of dialkyl phthalates, cycloalkyl phthalates, benzyl and arylphthalates, alkoxy phthalates, alkyl/aryl phosphates, carboxylic acidesters, polyglycol esters, adipate esters, citrate esters, and esters ofglycerin. Commercially available plasticizers with specific structurefound to be compatible include:

Acetates:

cumyl phenyl acetate;

Glyceryl Triacetate, triacetin;

Adipates:

dibutoxy ethoxy ethyl adipate

dibutoxy ethyl adipate

di iso butyl adipate

Citrates:

tri-n-ethyl citrate;

acetyl tri-n-ethyl citrate;

tri-n-propyl citrate;

acetyl tri-n-propyl citrate;

tri-n-butyl citrate;

acetyl tri-n-butyl citrate;

Phthalates:

DBP, dibutyl phthalate (partial compatibility);

BBP, butyl benzyl phthalate (total compatibility);

DBEP dibutoxy ethyl phthalate (partial compatibility);

2 ethyl hexyl benzyl phthalate;

tetramethyl oxa onononyl benzyl phthalate;

Benzoates:

dipropylene glycol dibenzoate;

diethylene glycol dibenzoate;

50/50 blend dipropylene glycol dibenzoate and diethylene glycoldibenzoate;

1,4 cyclohexane dimethanol dibenzoate;

glyceryl tribenzoate;

cumyl phenyl benzoate;

neopentyl glycol dibenzoate;

pentaerythritol tetabenzoate;

Phosphates:

butyl phenyl diphenyl phosphate;

TCP, tricresyl phosphate;

2 ethylhexyl diphenyl phosphate;

isodecyl diphenyl phosphate;

C12, C16 alkyl diphenyl phosphate;

isopropylated triphenyl phosphate;

Polyglycols:

Polyethylene glycols;

Polypropylene glycols.

Particularly preferred plasticizers have high thermal stability, andinclude: p-t-butylphenyl diphenyl phosphate; butyl benzyl phthalate;7-(2,6,6,8-tetramethyl-4-oxa-3-oxononyl)benzyl phthalate; C7/C9 alkylbenzyl phthalate; 2-ethylhexyl diphenyl phosphate; and isodecyl diphenylphosphate.

Optionally, the alkali-soluble support material B may contain othercomponents as well, such as filler materials. For example, inert fillersmay be selected from a polymer filler group consisting of calciumcarbonate, magnesium carbonate, glass spheres, graphite, carbon black,carbon fiber, glass fiber, talc, wollastonite, mica, alumina, silica,kaolin, whiskers and silicon carbide. Inorganic fillers such as solublesalts may also be used.

Techniques conventional in polymer chemistry are used to compound thecomponent materials into alkali-soluble support material B. Theformulation may be molded into rods, pellets or other shapes for use inthe extrusion apparatus, or it may be used directly in the apparatuswithout prior solidification. Alternatively, the mixture may besolidified and then granulated, for supply to the extrusion apparatus ingranulated form. For use in the modeling process shown and describedherein, a granulated feedstock composition is processed throughconventional extrusion apparatus to form continuous flexible filaments.Desirably, these filaments are wound in continuous lengths on a spooland dried. Alkali-soluble support material B in filament form issupplied to the extrusion apparatus 10 as described above. The filament20 is typically of a very small diameter, on the order of 0.070 inches,and may be as small as 0.001 inches in diameter.

EXAMPLES

The present invention is more particularly described in the followingexamples that are intended as illustrations only, since numerousmodifications and variations within the scope of the present inventionwill be apparent to those skilled in the art. Unless otherwise noted,all parts, percentages, and ratios reported in the following examplesare on a weight basis, and all reagents used in the examples wereobtained, or are available, from general chemical suppliers such as theSigma-Aldrich Chemical Company of Saint Louis, Mich., or may besynthesized by conventional techniques.

Example I

The alkali-soluble thermoplastic material contains 74% of the basepolymer and 26% of butyl phenyl diphenyl phosphate plasticizer. The basepolymer consists of a higher and a lower molecular weight copolymer ofmethacrylic acid and methyl methacrylate. The base polymer containsroughly 50% of the higher molecular weight copolymer and 50% of thelower molecular weight copolymer, plus or minus 5% of each. Eachcopolymer contains a 1:2 weight percent ratio of methacrylic acid tomethyl methacrylate. The higher molecular weight copolymer ischaracterized by a high viscosity (low melt flow), and the low molecularweight copolymer is characterized by a low viscosity (high melt flow).Melt flow of the copolymers is measured by plasticizing each copolymerseparately with 26 weight percent of the butyl phenyl diphenyl phosphateplasticizer. The melt flow index of the plasticized high molecularweight copolymer is in the range of 0.4 grams/10 minutes to 0.8 grams/10minutes, as measured pursuant to ASTM D1238 under a 1.2 kilogram load at230° C. The melt flow index of the plasticized low molecular weightcopolymer is in the range of 28 grams/10 minutes to 35 grams/10 minutes.The resulting thermoplastic composition has a melt flow index of 5grams/10 minutes to 6.5 grams/10 minutes and a glass transitiontemperature of about 90° C.

The alkali-soluble thermoplastic material is processed into a 0.070 inchdiameter filament and wound on a spool. The filament is fed to aStratasys FDM® 1650 or a Stratasys FDM® 2000 benchtop model machine. Themolten alkali-soluble thermoplastic material is extruded from aliquifier having a temperature of 200° C. into a 70° C. build envelopeonto a polyurethane foam base. The extruded alkali-soluble thermoplasticmaterial has a road width of about 0.020 inches to about 0.040 inchesand a road height (slice interval) of about 0.007 inches to about 0.020inches. A model is built from ABS thermoplastic having a glasstransition temperature of 104° C., using the alkali-solublethermoplastic material to form supports. The model with the attachedsupports is placed into an ultrasonic cleaning bath (having a scanningfrequency of 25-27 Hertz), containing an alkaline aqueous solution ofapproximately 98.7 weight percent water, 0.85 weight percent watersoftener, 0.30 weight percent pH adjuster and 0.15 weight percentsurfactant, resulting in a pH of 11 to 13. The bath temperature is setto 70° C. (the bath temperature must remain lower than the glasstransition temperature of modeling material A). In two hours time orless the supports are dissolved.

An alternative base polymer formulation combines the higher molecularweight 1:2 copolymer of methacrylic acid and methyl methacrylate with alower molecular weight copolymer containing 40% methacrylic acid and 60%butyl methacrylate. A further alternative base polymer formulation usesacrylic acid as the first comonomer. The further alternative was foundunacceptable for use in the Stratasys FDM® modeling machines, however,as it results in a base polymer having a lower glass transitiontemperature lower than the build envelope temperature of the machines.

Example II

The alkali-soluble thermoplastic material contains 79% (+/−5%) of thebase polymer and 21% (+/−5%) of butyl phenyl diphenyl phosphateplasticizer. The base polymer consists of a 1:1 weight percent ratio ofmethacrylic acid to methyl methacrylate, having a molecular weight of135,000 grams/mole. Prior to compounding the base polymer with theplasticizer, the base polymer is heated in a 220° C. oven at lowpressure to rid the polymer of water. Heating at low pressure for 10-15hours was found sufficient to dry the base polymer. The resultant drypolymer is in the form of granules, which are fed into a compounder withthe plasticizer in a known manner. The resulting alkali-solublethermoplastic material has a melt flow index in the range of 5 grams/10minutes to 6.5 grams/10 minutes, as measured pursuant to ASTM D1238under a 1.2 kilogram load at 230° C. The glass transition onsettemperature of the alkali-soluble thermoplastic material is about 101.5°C. and the glass transition peak temperature is about 111° C.

As in Example I above, the alkali-soluble thermoplastic material isprocessed into a 0.070 inch diameter filament and wound on a spool. Thefilament is fed to a Stratasys FDM® 1650 or a Stratasys FDM® 2000benchtop model machine. Molten alkali-soluble thermoplastic material isextruded from a liquifier having a temperature of 235° C. into a buildenvelope having a temperature of 70° C. to 80° C., onto a polyurethanefoam base. The extruded alkali-soluble thermoplastic material has a roadwidth of about 0.020 inches to about 0.040 inches and a road height(slice interval) of about 0.007 inches to about 0.020 inches. A model isbuilt from ABS thermoplastic having a glass transition temperature of104° C., using the alkali-soluble thermoplastic material to formsupports. To dissolve the supports, the model is placed into anultrasonic cleaning bath set to 70° C. and having a scanning frequencyof 25-27 Hertz, containing an alkaline aqueous solution of approximately98.7% water, 0.85% water softener, 0.30% pH adjuster, and 0.15%surfactant. In two hours time or less the supports are dissolved. Thealkali-soluble thermoplastic material according to this example exhibitsthermal properties, mechanical strength, viscosity, adhesion, solubilityand processing characteristics suitable for three-dimensional modelingon the Stratasys filament-feed benchtop machines.

Example III

The alkali-soluble thermoplastic material has the same composition as inExample II above, but in this example the base polymer is not heated torelease moisture. The alkali-soluble thermoplastic material is processedand extruded from a Stratasys FDM® machine as in Example II, anddeposited to form a support structure for a model built of ABSthermoplastic. In this example, the alkali-soluble thermoplasticmaterial exhibited a greater amount of “ooze” from the extrusion headthan is desirable, but otherwise exhibited characteristics suitable forthree-dimensional modeling. The “ooze” is attributable to water presentin the composition. If used in a modeling system wherein the materialdispenser has a positive cut-off mechanism, the “ooze” effect exhibitedin the Stratasys FDM® machine would not occur and the material accordingto this Example III could be effectively utilized.

Example IV

Samples of alkali-soluble thermoplastic materials of the presentinvention were created with varying concentrations of plasticizer tocompare the effects of the plasticizer on the glass transitiontemperatures and the melt flow indexes. The base polymers and theplasticizers used were the same as described in Example I. Table 1provides the weight percent concentrations of the alkali-solublethermoplastic materials of Examples IV(A)-Examples IV(M). As shown, theconcentration of plasticizer was varied between the samples. Table 1also provides the corresponding glass transition temperatures (Tg) andthe melt flow indexes (MFI) of the alkali-soluble thermoplasticmaterials of Examples IV(A)-Examples IV(M). The melt flow indexes weretested pursuant to ASTM D1238 under a 1.2 kilogram load at 160° C., 230°C., or 270° C.

TABLE 1 Weight Percent Weight Percent Tg MFI MFI MFI Composition BasePolymer (*) Plasticizer (*) (° C.) (160° C.) (230° C.) (270° C.) ExampleIV(A) 100 0 160 Example IV(B) 98 2 156 1.1 Example IV(C) 97 3 154 1.2Example IV(D) 96 4 147 1.6 Example IV(E) 95 5 145 2.5 Example IV(F) 93 7142 3.4 Example IV(G) 90 10 134 6.0 Example IV(H) 83 17 116 1.7 ExampleIV(I) 81 19 111 2.3 Example IV(J) 79 21 109 3.0 Example IV(K) 75 25 1006.2 Example IV(L) 65 35 74 35.0 Example IV(M) 55 45 49 5.1 (*) Based ofthe total weight of the alkali-soluble thermoplastic material.

The data in Table 1 illustrates the effects of the plasticizerconcentration on the glass transition temperature and the melt flowindex of the alkali-soluble thermoplastic materials. In general, as theconcentrations of plasticizer in the alkali-soluble thermoplasticmaterials increase, the glass transition temperatures decrease and themelt flow indexes increase. As such, varying the plasticizerconcentration provides a trade-off between the glass transitiontemperature and the melt flow index.

For the base polymer and plasticizer used for Examples IV(A)-ExamplesIV(M), the glass transition temperatures ranged from about 49° C. (45%plasticizer) to about 160° C. (no plasticizer), and were generallyinversely linear to the concentration of plasticizer. As discussedabove, the alkali-soluble support materials of the present inventiondesirably exhibit glass transition temperatures at least 10° C. abovethe build envelope temperatures. As such, when using high build envelopetemperatures (e.g., 100° C. or higher), alkali-soluble thermoplasticmaterials with low concentrations of plasticizer are preferred (e.g.,25% or less) to allow the alkali-soluble thermoplastic materials toexhibit higher glass transition temperatures.

With respect to the melt flow index tested at 230° C., the data in Table1 shows that the melt flow index increases generally in an exponentialmanner relative to the concentration of plasticizer. An increase from25% to 35% plasticizer caused the melt flow index to increase from about6 grams/10 minutes to about 35 grams/10 minutes. As discussed above, amelt flow index ranging from about 1 gram/10 minutes to about 10grams/10 minutes is preferred. As such, a melt flow index of about 6grams/10 minutes is considered acceptable conditions for extruding thematerial. However, a melt flow index of about 35 grams/10 minutes maycause the desired physical properties to potentially deteriorate.

As shown in Table 1, plasticizer concentrations of about 25% or less(Examples IV(A)-Examples IV(K)) provide glass transition temperatures ofabout 100 C or greater, and melt flow indexes of about 6 grams/10minutes or less at 230° C. Such plasticizer concentrations provideacceptable physical characteristics for the alkali-soluble thermoplasticmaterials of the present invention.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention. For example, it will be appreciated thatinnumerable modifications may be made to the modeling process. It willfurther be appreciated that various modifications may be made to thecomposition. Also, the thermoplastic material of the present inventioncould be used to create an alkali-soluble three-dimensional objecthaving usefulness in various molding processes. For example, thealkali-soluble material can form a dissolvable master core in a cast orinjection process. The alkali-soluble material can likewise be used tocreate a mold (by deposition modeling or otherwise), which mold canlater be dissolved out of an object formed by molding processes.

1. A support material feedstock for making a support structure for a three-dimensional object using an additive processing technique, the support material feedstock comprising: a composition comprising: at least one copolymer comprising: a plurality of pendent carboxylic acid groups derived from monomers comprising methacrylic acid; and a plurality of pendent ester groups derived from alkyl methacrylates; and at least one plasticizer, wherein the composition is soluble in an alkaline aqueous solution; and a filament geometry configured to be received by a filament-fed extrusion system configured to make the support structure in a layer-by-layer manner in coordination with the three-dimensional object using the additive processing technique.
 2. The support material feedstock of claim 1, wherein the alkyl methacrylate comprises methyl methacrylate.
 3. The support material feedstock of claim 1, wherein the composition consists essentially of the at least one copolymer and the at least one plasticizer.
 4. The support material feedstock of claim 1, wherein the composition exhibits a melt flow index ranging from of about 1 gram/10 minutes to about 10 grams/10 minutes when tested pursuant to ASTM D1238 under a 1.2 kilogram load at 230° C.
 5. The support material feedstock of claim 1, wherein the at least one plasticizer constitutes from about 10% by weight to about 30% by weight of the composition, based on a total weight of the composition.
 6. The support material feedstock of claim 1, wherein the at least one plasticizer comprises an aromatic plasticizer.
 7. A method of forming the support material feedstock of claim 1 , the method comprising: providing the at least one copolymer wherein the plurality of pendent carboxylic acid groups constitute from about 15.0% to about 60.0% by weight of pendent groups of the copolymer, based on a total weight of the pendent groups of the at least one copolymer; combining the at least one copolymer with the at least one plasticizer to form a composition, the at least one plasticizer constituting from about 10% by weight to about 30% by weight of the composition, wherein the composition is soluble in an alkaline aqueous solution; and forming the support material feedstock from the composition, the formed support material feedstock having a filament geometry that is configured to be received by a filament-fed extrusion system configured to make the support structure in a layer-by-layer manner in coordination with a three-dimensional object using an additive processing technique.
 8. The method of claim 7, and further comprising drying the formed feedstock to remove moisture from the formed feedstock.
 9. The method of claim 7, and further comprising winding successive portions of the formed feedstock onto a spool that is configured to supply the formed feedstock to the filament-fed extrusion system.
 10. A method of building a three-dimensional object with an extrusion system, the method comprising: heating a build envelope of the extrusion system to one or more elevated temperatures; dispensing a thermoplastic material in the heated build envelope using an additive processing technique to form the three-dimensional object in a layer-by-layer manner, the three-dimensional object having at least one overhanging feature; feeding the support material feedstock of claim 1 to an extrusion head of the extrusion system; melting the support material feedstock in the extrusion head to a flowable state; dispensing the melted support material in the heated build envelope in coordination with the dispensing of the thermoplastic material, using the additive processing technique to form a support structure in a layer-by-layer manner configured to support the at least one overhanging feature of the three-dimensional object; and exposing the formed support structure to an alkaline aqueous solution to at least partially remove the formed support structure from the formed three-dimensional object.
 11. The method of claim 10, wherein the support material feedstock comprises a filament geometry.
 12. The method of claim 10, wherein the at least one plasticizer constitutes from about 10% by weight to about 30% by weight of the composition of the support material, based on a total weight of the composition of the support material. 